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Most of these problems are due to faults in the horizontal deflection system - shorted HOT, shorted windings or HV rectifiers in the flyback, defective tripler, or other bad parts on the primary side of the flyback. In addition, with auto-scan monitors, the incorrect voltage or other component could be selected due to a logic fault or a problem with the selection relay or other circuitry. However, if you discover an inch layer of filth inside the monitor, the HV could simply be shorting out - clean it first. In most cases, these sorts of faults will put an excessive load on the horizontal output circuits so there may be excessive heating of the HOT or other components. You may hear an audible arcing or sizzling sound from internal shorts in the flyback or tripler. Either of these may bet hot, crack, bulge, or exhibit visible damage if left on with the fault present. Many modern monitors do not regulate HV directly but rather set it via control of the low voltage power supply to the HOT (B+), by snubber capacitors across the HOT, and the turns ratio of the flyback. The HV is directly related to the B+ so if this is low, the HV will be low as well. Faulty snubber capacitors will generally do the opposite - increase the HV and the X-ray protection circuits may kick in. However, low HV is also a possibility. The only way the turns ratio of the flyback can change is from a short which will manifest its presence in other ways as well - excessive heating and load on the horizontal output circuits. While a shorted second anode connection to the CRT is theoretically possible, this is quite unlikely (except, as noted, due to dirt).
Any significant increase in HV should cause the X-ray protection circuits to kick in and either shut down the set or modify the deflection in such a way as to render it harmless. Symptoms include arcing/sparking of HV, smaller than normal picture, and under certain scenarios, possible excessive brightness. Causes of the HV being too high are: 1. Excess B+ voltage to the HOT. The likely cause is to a low voltage regulator failure. 2. Open snubber capacitors across the HOT. These are under a lot of stress and are located near hot components so failure is possible. 3. Incorrect excessively long scan drive to HOT caused by failure of horizontal oscillator/sync circuits. However, other things like the HOT will probably blow up first. The picture will definitely be messed up. This is more likely with auto-scan monitors than TVs since what is too long for one scan range may be correct for another and the selection circuitry is confused or broken. 4. Failure of HV regulator. Actual HV regulators are uncommon today but the HV may controlled by a feedback voltage from a divider (focus or screen, or its own) or a secondary winding on the flyback setting the B+ or drive timing. This may result in an underscanned (smaller than normal) picture if only the HV and not the deflection voltages as well are derived from the same supply. In one example of (4), a arcing of the HV in a Conrac studio monitor resulted in the destruction of the HV switchmode inverter transistor (this used a separate HV supply) and a fusable resistor. The cause was an open HV feedback resistor divider allowing the HV to increase drastically.
Various problems can result in occasional or sustained sparking or arcing sounds from inside the monitor. Note that a static electricity buildup is common on the front of the screen. It is harmless and there iss nothing you can do about it anyhow. The following may result in occasional or sustained sounds not commonly associated with a properly working TV or monitor. There may or may not be flashes or blanking of the screen at the same time as the audible noise. See the same-named sections that follow for details. * Arcing, sparking, or corona from CRT HV anode (red wire/suction cup). * Arcing at CRT sparkgaps. * Arcing from flyback or vicinity. * Arcing due to bad connections to or disconnected CRT return. * Flashovers inside the CRT.
Symptoms could include a sizzling corona or more likely, an occasional or rapid series of sharp snaps - possibly quite loud and quite visible - from the anode cap on the CRT to the grounded coating on the outside of the CRT or a chassis ground point (or any other conductor nearby). Corona is a high resistance leakage through the air without total breakdown. The snapping is caused by the sudden and nearly complete discharge of the CRT anode capacitance through a low resistance ionized path similar to lightning. There are two likely causes: 1. Dirt, dust, grime, around and under the suction cup on the CRT are providing a discharge path. This may be more severe in humid weather. Safely discharge the HV and then remove and thoroughly clean the HV suction cup and the area under it and on the CRT for several inches around the HV connection. Make sure there are no loose wires or other possible places for the HV to discharge to in the vicinity. 2. The high voltage has gone through the roof. Usually, the X-ray protection circuitry should kick in but it can fail. If cleaning does not help, this is a likely possibility. See the sections: "High voltage shutdown due to X-ray protection circuits" and "Excessive high voltage".
These are protective devices intended to breakdown and divert excessive voltage away from the CRT (usually). This is rarely due to a defective sparkgap or gas discharge tube but rather is a safety mechanism like a fuse designed to protect the internal electrodes of the CRT if the focus or screen voltage should become excessive. The sparkgap breaks down first and prevents internal arcing in the CRT. These sparkgaps may be built into the CRT socket as well. Arcing at a sparkgap or a glowing or flashing discharge tube may be accompanied by total loss of picture or bad focus, brightness or focus fluctuations, or any of a number of similar symptoms. A common cause is a breakdown inside the focus divider (usually part of the flyback or tripler) but could also be due to excessive uncontrolled high voltage due to a failure of the B+ regulator or HOT snubber capacitor, or (ironically) even a short inside the CRT. * Spark gaps may be actual two or three pin devices with seemingly no insides, part of the CRT socket, or printed on the circuit board itself. * Gas discharge tubes look like small neon lamps (e.g., NE2) but could be filled with some other gas mixture to provide a controlled higher breakdown voltage. Therefore, like a fuse, don't just replace or disable these devices, locate and correct underlying problem. The CRT makes an expensive fuse!
Arcing may be visible or audible and result in readily detectable levels of ozone. Note that very slight traces of ozone may not indicate anything significant but if the TV smells like an office copier, there is probably some discharge taking place. WARNING: It is possible for arcing to develop as a result of excessive high voltage. Symptoms might be a smaller than normal excessively bright picture but this may not be able to be confirmed until the flyback is repaired or replaced. See the section: "Excessive high voltage". * On the HV output, it will probably be a loud snapping sound (due to the capacitance of the CRT) with associated blue/white sparks up to an inch or more in length. If the arc length is short enough, this may turn into a nearly continuous sizzling sound with yellow/orange arc and melting/burning plastic. * Prior to the HV rectifier, it will likely be a continuous sizzle with orange/yellow/white arc and melting/burning plastic or circuit board material. * Internal arcing in the flyback may be audible and eventually result in a bulging and/or cracked case (if some other component doesn't fail first as this would take some time to develop). * A corona discharge without actual sparks or a visible well defined arc is also possible. This may be visible in a totally dark room, possibly more likely when the humidity is high. A thorough cleaning to remove all dust and grime may be all that is needed in this case. * If the arc is coming from a specific point on the flyback - a crack or pinhole - this may be patched well enough to confirm that the rest of the monitor is operational and a new flyback is worth the money. Otherwise, there is no way of knowing if the arcing may have damaged other circuitry until a replacement flyback - possibly money wasted - arrives. To attempt a repair, scrape off any dirt or carbon that is present along the path of the arcing and its vicinity. Then, clean the area thoroughly with alcohol and dry completely. Otherwise, the dirt and carbon will just act as a good conductor and the arcing will continue under your repair! Several layers of plastic electrical tape may be adequate for testing. Multiple coats of high voltage sealer or non-corroding RTV silicone (if it smells like viniger - acetic acid - as it cures, this may get in and affect the windings) would be better if the objective is an actual repair. This may prove to be a permanent fix although starting the search for a source for a new flyback would not hurt just in case. The arc most likely did damage the insulation internally which may or may not be a problem in the future. Also see the section: "Dave's complete procedure for repair of an arcing flyback". * In some cases, the pinhole or crack is an indication of a more serious problem - overheating due to shorted windings in the flyback or excessive secondary load. * If the arc is from one of the sparkgaps around the CRT or the CRT socket, this could also be a flyback problem indicating internal shorts in the focus/screen network. * If the arcing is inside the CRT, this could indicate a bad CRT or a problem with the flyback focus/screen network and no or inadequate sparkgap protection. Where repair seems possible, first, clean the areas around the arc thoroughly and then try several layers of plastic electrical tape. If the TV works normally for say, an hour, then there is probably nothing else wrong and you can try for a proper sealing job or hope that tape holds out (put a few more layers on - each is good for about 8-10 KV theoretically). Once I had a TV where the main problem was a cracked flyback arcing but this took out one of the fusable resistors for the power supply to the *vertical* output so the symptoms included a single horizontal line. Don't ask me to explain - replacing that resistor and the flyback (the flyback tested good, but this was for someone else) fixed the TV. In another case, a pinhole developed in the flyback casing probably due to poor plastic molding at the time of manufacture. This resulted in a most spectacular case of sparking to a nearby bracket. A few layers of electrical tape was all that was needed to affect a permanent repair. However, replacement is really the best long term solution both for reliability as well as fire risk. (From: Bert Christensen (rosewood@interlog.com)). It may well last a long time. The insulation breakdown was probably in the area of the rectifier section rather than the flyback section. I have repaired several units in the same way but I have generally replaced the flyback before sending back to the customer. I am worried that the repair will not hold and that a fire could start. I have no desire whatsoever to be sued by some fire insurance company. I am always reminded by the experience that Zenith had with its System 3 chassis a few years ago. They burned and caused many house fires including one in the governor's mansion in Texas. Zenith spent mega bucks on that one. They also spent mega-bucks on their 'safety capacitor' mess a few years before that.
(From: Dave Moore (penguin@datastar.net). First I clean the afflicted area with Electromotive spray from Autozone. It's for cleaning alternators. On Z-line I remove the focus control and wash with the alternator cleaner and a tooth brush until all dirt and carbon deposits are removed. Then I take an xacto knife and carve out the carbonized hole where the arcing broke through. Then take your soldering iron and close the hole by melting adjacent plastic into it. (clean any solder off your iron with solder-wick first). Then cut some plastic off of some other part off the flyback where it wont be needed and use this to plastic weld (with your iron) a hump of a patch into and over the arc hole. Smooth and seal with iron. Next apply as thick a layer of silicone rubber as you can and let dry overnight.
These are protective devices intended to breakdown and divert excessive voltage away from the CRT (usually). * Spark gaps may be actual two or three pin devices with seemingly no insides or printed on the circuit board itself. * Gas discharge bulbs look like small neon lamps (e.g., NE2) but could be filled with some other gas mixture to provide a controlled higher breakdown voltage. Arcing at a spark gap or a flashing or glowing gas discharge tube may indicate excessive high voltage, a short in the focus/screen divider network of the flyback, a short in the CRT, or some other fault resulting in abnormally high voltage on its terminals.
The Aquadag coating on the outside of the CRT is the negative plate of the HV filter capacitor. If this is not solidly connected to the HV return, you will have your 25 KV+ trying to go where it should not be. There should be a wire solidly attached to the CRT neck board or chassis. Without this, voltage will build up until it is able to take some other path - possibly resulting in damage to sensitive solid state components in the process. Therefore, is is important to rectify the situation. Warning: If you find this disconnected, don't just attach it anywhere. You may instantly kill ICs or other solid state components. It must be connected to the proper return point on the CRT neck board or chassis.
Due to sharp edges on the electron gun electrodes, impurities, and other manufacturing defects, there can be occasional arcing internal to the CRT. Properly designed HV, deflection, and power supply circuits can deal with these without failing but not all monitors are designed well. There is nothing you can do about flashovers assuming your HV is not excessive (see the section: "Excessive high voltage". If these persist and/or become more frequent, a new CRT or new monitor will be needed.
Smoking is just as bad for monitors as for people and usually more quickly terminal (no pun....). White acrid smoke may indicate a failed electrolytic capacitor in the power supply probably in conjunction with a shorted rectifier. Needless to say, pull the plug at once. A visual inspection should be able to easily confirm the bad capacitor as it will probably be bulging and have condensed residue nearby. Check the rectifier diodes or bridge rectifier with an ohmmeter. Resistance across any pair of leads should be more than a few ohms in at least one direction. Remove from the circuit to confirm. Both the faulty diode(s) and capacitor should be replaced (though the capacitor may work well enough to test with new diode(s). If a visual inspection fails to identify the smoking part, you can probably plug the monitor in for a few seconds until the source of the smoke is obvious but be prepared to pull the plug in a real hurry. If the smell/smoke is coming from the flyback, then it has probably gone belly up. You may be able to see a crack or bulge in the case. While the flyback will definitely need to be replaced, it is likely that nothing else is wrong. However, it might be prudent to use a Variac when performing initial testing with the replacement just in case there is a secondary short circuit or excess HV problem.
X-ray radiation is produced when a high velocity electron beam strikes a target containing heavy metals. In a modern monitor, this can only take place at the shadow mask/aperture grille and phosphor screen of the CRT. For X-rays, the amount of radiation (if any) will be proportional to brightness. The energy (determined by the CRT high voltage, called KVP in the medical imaging field) is not affected. This is one reason many monitors and TVs are designed with brightness limiting circuits. In any case, there will be virtually no X-ray emissions from the front of the CRT as the glass is greater than an inch thick and probably contains some lead for added shielding. Also see the section: "Should I be worried about X-ray exposure while servicing a TV or monitor?". Electromagnetic radiation (EM) is produced mostly from the deflection yoke and to a lesser extent from some of the other magnetic components like transformers and inductors. Depending on monitor design (some are specifically designed to reduce this), EM emissions can vary quite a bit. Frequencies range from the 50/60 Hz of the power line or vertical scan rate to several hundred KHz in the AM broadcast band. The intensity and spectral distribution will vary depending on horizontal and vertical scan rate. A totally black screen will reduce X-ray emission to zero. It will not affect EM emissions significantly as most of this comes from the magnetic parts, particularly the deflection yoke. There is no measurable microwave, IR, or UV radiation. I refuse to get into the discussion of what, if any, health problems result from low level EM emissions. There is simply not enough data.
The only source of X-rays in a modern TV or monitor is from the CRT. X-rays are generated when a high velocity electron beam strikes a heavy metal target. For anything you are likely to encounter, this can only happen in a vacuum - thus inside the CRT. The higher the voltage, the greater the velocity and potential danger. Really old TVs (prior to around 1975) may still have HV rectifier and regulator tubes - other sources of X-rays. However, modern TVs and monitors implement these functions with solid state components. The thick front CRT faceplate protects users adequately but there may be some emission from the thinner sides. At 25-30 KV (quite low as X-ray energies go) X-rays will be stopped by almost any metal so what you have to worry about is where there are no shields. In addition, the CRT glass usually contains some lead compounds to block X-ray emissions. However, realistically, there is very little danger. I would not worry about exposure unless you plan to be sitting for hours on the sides, behind, or under the TV or monitor - with a picture (there will be none if the screen is black). It is interesting that even those 1.5" Watchman and .5" camcorder viewfinder CRTs have X-ray warning labels even though the high voltage used with these isn't anywhere near high enough to be of any concern!
You put your can of Coke where???? Who says these FAQs cannot be funny? Needless to say, unplug the monitor immediately. Inspect around the target area for obviously blown or damaged components. Test fuses and fusable resistors. Remove all traces of liquid - especially sugary or corrosive liquid. Use water first and then alcohol to promote drying. Repair burnt solder connections and circuit board traces. Once the monitor is entirely dried out, power it up - preferably through a series light bulb and/or Variac until you are sure nothing else will let loose. Look, listen, and smell for any unusual behavior. If it now works, then consider yourself lucky. If not, there may be damage to transistors, ICs, or other components. Another cause of this is using spray cleaner or a too wet rag on the front of the CRT (other parts of the monitor, for that matter). Any liquid which drips inside (all too likely) may short out circuitry on the mainboard with very expensive consequences.
There are several symptoms that are basically similar: * Blooming is defined as an expansion of the raster or horizontal sections of the raster with bright material. For example, switching between dark and light picture causes the size of the picture to expand by 10%. A slight change in size is unavoidable but if it is greater than 1 or 2 percent from a totally black image to a full white one, this is either an indication of a defective monitor or one that is badly designed. The cause is poor low or high voltage regulation. Check the B+ to the horizontal deflection. This is usually well regulated. If it is varying in sympathy to the size changes, trace back to determine why the low voltage regulator is not doing its job. The reason for the size change is that the high voltage is dropping and reducing the stiffness of the electron beam. * Expansion of the raster width in areas of bright imagery is an indication of short term regulation problems. The video drive may be interacting with the other power supplies. Check for ripple - this would be at the vertical scan rate - in the various regulated power supplies. The cause may be a dried up electrolytic capacitor - once you locate the offending voltage, test or substitute capacitors in that supply. In both these cases, if this just started after some work was done to the monitor, the brightness limiter and/or video drive may simply be set so high that the monitor cannot supply enough current to the high voltage. If the brightness is acceptable with these turned down slightly and still have acceptable brightness, then there may be nothing wrong. * Breathing is defined as a periodic change in the size of the raster which may be independent of what is displayed or its severity or frequency may be related to the brightness or darkness of the image. This is another type of regulation problem and may be caused by bad electrolytic capacitors or other components in the low voltage power supplies. If the monitor uses a switchmode power supply or low voltage regulator separate from the horizontal deflection, first check its output(s) for a variation in voltage at the breathing rate. Test with a light bulb or resistor load to confirm that the problem is here and not the deflection or remainder of the monitor. * A condition with somewhat similar symptoms is bad focus - fuzzy picture - but only with bright (high beam current) scenes. This could be just a matter of adjusting the focus control but may also indicate sub-optimal filament voltage due to bad connections or components in the filament circuit, or a tired worn CRT. You won't get high beam current without some serious spot blooming (a fat beam because too much cathode area is used) and you will get cathode 'poisoning' after prolonged use. Visually inspect the neck of the CRT for the normal orange glow of the filaments and check for bad connections and bad parts.
Symptoms may include fluctuating focus or brightness. In extreme cases, the result may be a too bright or dark picture or other behavior caused by breakdown in the Focus/Screen(G2) divider network. Usually, this will require flyback replacement to repair reliably. Sometimes, the section with the controls can be snapped apart and cleaned but this is not common. First, just try rotating the screen (G2) control back and forth a few times. This may clean up the contacts and eliminate the erratic behavior. Possibly, positioning it a bit to one side of the original location will help. Then, use the individual or other master background/bias adjustments to compensate for the improper brightness. If this doesn't help, here is a 'well it's going in the dumpster anyhow' procedure to try: After discharging the CRT (so you don't get zapped) drill a tiny hole in the plastic cover near the bad control. Be careful you don't damage anything inside - you just want access to the contacts of the controls. Use a hand drill with, say, a 1/16" bit. Don't drill more than about 1/8" deep which should enter the airspace. Then spray some contact cleaner through the hole and work the controls. Wait sufficient time for the everything to dry COMPLETELY and see if behavior changes (or it works at all). This is a 'you have got to be kidding' type of repair so no guarantees :-). If by some miracle it does work, fill the hole with a drop of RTV or just put a couple of layers of electrical tape over it.
This is kludge number 41256 but may be the difference between a bit more life and the dumpster. If the previous extreme measures don't help, then it may be possible to simply substitute a good divider network externally. Note that if there is evidence of internal breakdown in the divider of the original flyback (hissing, cracks, overheating, bulging case, etc.), this will not work unless you can disconnect it from its HV connection. There are two issues: 1. Is this a stable situation? Even if you provide an external substitute, the parts inside the flyback may continue to deteriorate eventually resulting in other more total failure of the flyback or worse. 2. If you provide an external focus/screen divider, it must be done is such a manner (including proper mounting and super insulation) such that it cannot be called into question should there be a fire where the monitor is even the slightest bit suspect. Various size external focus/screen divider networks can be purchased but whether this is truly a cost effective solution is not obvious. (From: Larry Sabo (sabo@storm.ca)). I just ordered a 'bleeder resistor' from Data Display Ltd (Canadian sub of CCS) to use as a cure for flybacks with flaky focus/screen pots. It contains focus and screen pots, and costs Cdn$ 16.99, which is a lot less than a complete flyback, that's for sure. I expect it will be compatible with quite a wide range of flybacks. I have used bleeder resistor assemblies from duff flybacks a couple of times with good success. You connect the HV lead into the HV cap of the original flyback, ground all pins of the sub flyback, and use the focus and screen leads from the sub bleeder assembly in place of the originals. Looks like hell but works fine. Mounting (and securing) the substitute is a challenge given the limited space available. I only use this approach on what would otherwise be uneconomical to repair, and always advise the owner or customer of the cobbling job. It also enables you to verify whether it is the flyback that needs replacement, versus the CRT.
The following applies to both CRT focus voltage (which should be a few KV) and screen or G2 voltage (which should be several hundred V). "The screen voltage will come up to normal after sitting over night, 400 V or so. After approximately 5 minutes or slightly longer, I hear a slight arcing. From that point on, the screen voltage will wander anywhere from 75 V up to maybe 150 V. Adjustment of the screen control on the flyback has only a small effect and is not permanent. Removing the CRT pcb results in the screen voltage returning to normal." This is very likely a short between electrodes inside the CRT unless there is something on the neck board that is breaking down as a result of some connection to the CRT. The flyback should largely not know the difference with the socket plugged into the CRT. One possibility is that glue used to hold components down on some circuit boards has deteriorated and turned conductive. Check for tan to brown stuff shorting traces on the CRT neck board. If this is present on the focus or screen traces or wires, it may just be your problem. Scrape off all of the old glue and then clean thoroughly. Repair any damaged traces. What happens to the HV? A HV breakdown possibly inside the CRT would result in all the voltages being dragged down. What happens to the picture? If you connect a charged HV capacitor (guessing a couple hundred volts, a couple microfarads) between G2 and G1 or focus, you **will** know if tapping the neck results in a momentary short! I cannot predict whether this will be a temporary cure or permanent killer. See the section: "Rescuing a shorted CRT". Here is another thing to try: put a 100 M ohm or so resistor between SCREEN and the CRT socket. This should not affect the behavior much until the failure occurs. Then, check the voltage on both sides with a high impedance voltmeter (1000 M). If the CRT is arcing, it will be much lower on the CRT side and will probably fluctuate. You can play similar games with focus voltage.
In some cases, the focus wire - the not-so-fat wire from the flyback or focus divider - may terminate directly in the CRT socket with no obvious means of freeing it should flyback replacement be needed. One alternative is simply to cut the wire in a location that is well away from any place to short out, solder, and then do a most excellent job of insulating the splice. However, you may find that the cap on the CRT socket snaps off using a thin knife blade or screwdriver. The wire may be soldered or just pressed in place in such a way that pulling it out is difficult or impossible without removing the cover. (From: Raymond Carlsen (rrcc@u.washington.edu)). The last one I worked on puzzled me for a few moments. See if you can see a space between the little cup (where the wire enters the socket) and the socket itself. Pry up on the cap with a knife and it should pop right off. The wire is soldered to a pin under it. Don't apply heat for very long... you may melt the socket.
"I have a 3-5 yr old monitor that loses screen voltage. I believe that the problem is specific to the CRT or the flyback, either one is a guess I'd rather be sure of prior to ordering a part. The screen voltage will come up to normal after sitting over night, 400 V or so. After approximately 5 minutes or slightly longer, I hear a slight arcing. From that point on, the screen voltage will wander anywhere from 75 V up to maybe 150 V. Adjustment of the screen control on the flyback has only a small effect and is not permanent. Removing the CRT pcb results in the screen voltage returning to normal. I cannot find the source of the arcing, as it happens quickly and I have always been on the other side of the set when it happens. I have replaced the crt socket, thinking the spark gap was arcing. I have checked the CRT for G1 and HK shorts on a sencore crt checker, it checks good, but I am aware that since it is an intermittent problem, that the checker probably will not catch it." This sounds like a CRT short unless there is something on the neck board that is breaking down. The Sencore may not provide the same high voltages as normal screen (several hundred volts) or focus (several thousand volts). The flyback should largely not know the difference whether the screen or focus electrode of the CRT is connected or not. The current should be negligible. One possibility is that glue used to hold components down on some circuit boards has deteriorated and turned conductive. Check for tan to brown stuff shorting traces on the CRT neck board. If this is present on the focus or screen traces or wires, it may just be your problem. Scrape off all of the old glue and then clean thoroughly. Repair any damaged traces. What happens to the HV? A HV breakdown possibly inside the CRT would result in all the voltages being dragged down. What happens to the picture? If you connect a charged HV capacitor (guessing a couple hundred volts, a couple microfarads) between G2 and G1 or focus, you **will** know if tapping the neck results in a momentary short! I cannot predict whether this will be a temporary cure or permanent killer. Here is another thing to try: put a 100 M ohm or so resistor between SCREEN (or FOCUS) and the CRT socket. This should not affect the behavior much until the failure occurs. Then, check the voltage on both sides with a high impedance voltmeter (>1000 M). If the CRT is arcing, it will be much lower on the CRT side.Go to [Next] segment
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